Since, notwithstanding the availability of voluntary safety devices such as lap and shoulder belts, large numbers of people are killed or maimed annually in motor vehicle accidents wherein the occupants are thrown forwardly within the vehicle so as to collide with the solid interior surfaces thereof, there has been considerable impetus toward the development of motor vehicle passive restraint systems. One system extensively investigated senses rapid deceleration of the vehicle, such as that which occurs upon impact, and initiates inflation of a bag between, for example, the steering wheel and the driver. Inflation of the bag must therefore occur within milliseconds of the impact in order to restrain the driver before he can be thrown against the solid interior surface of the vehicle.
As soon as the initial or primary impact of a crash is completed, it is desirable to deflate the bag so that the driver is not trapped in the vehicle by an inflated bag. Moreover, it is further desirable that the bag be deflated rapidly so that, in the event, for example, of an accidental inflation, the restraint upon the person driving the automobile is sufficiently short that he does not lose control of the vehicle. In order to meet such criteria, the bag must be sufficiently inflated to restrain a passenger in about 30-60 milliseconds after the initiation of inflation and substantially deflated after about 100 milliseconds.
Generally, such passive restraint airbag systems include a pressurized fluid source of any conventional type, i.e. (a) stored gas, (b) a pyrotechnic inflator or (c) a hybrid, i.e, combination system. When the assembly is arranged to protect the driver of the vehicle, the source may be mounted on the steering wheel or the steering column, or it may be mounted remote from either and connected by conduit means to the inflatable cushion. The sensor which actuates the pressurized fluid source is normally mounted remote from the steering apparatus in order to sense impacts received by the vehicle or the probability or possibility of such impacts.
A further advance in the field of passive motor vehicle crash restraints involves the inclusion of aspiration means which draws air from within the vehicle's passenger compartment into the air bag so as to both cool the gas entering the bag from a fluid source such as a pyrotechnic inflator operatively associated therewith and to permit a more rapid inflation of the air bag than would otherwise be possible utilizing only the gas produced by the inflator device.
Various types of aspirating inflators are known and used in the prior art. For example, a number of references disclose arrangements wherein the interior of the bag communicates with the atmosphere within the vehicle's passenger compartment through a unidirectional valve. Such valves permit air from the passenger compartment to enter the interior of the bag, thus facilitating the inflation of the bag, but these valves thereafter prevent the atmosphere within the bag from venting back into the passenger compartment. Examples of air bag systems of the type described above may be found in U.S. Pat. Nos. 3,675,942 to Huber; 3,767,225 to Mazelsky; 3,773,350 and 3,791,666 to Shibamoto; 3,788,663 to Weman; and 3,909,037 to Stewart.
Alternately, a number of references disclosed air bag inflation devices wherein the flow of ambient atmosphere proceeds in two directions, i.e., initially, from the passenger compartment into the air bag and then, subsequent to the collision, gradually back into the passenger compartment so as to facilitate the deflation of the air bag. Air bag devices of this type are found, for example, in U.S. Pat. Nos. 3,762,741 and 3,784,225 to Fleck et al.; 3,773,351 to Catanzarite; 3,843,152 to Nonaka and 3,910,595 to Katter et al.
In a further alternate arrangement, the ambient air from the passenger compartment is initially aspirated into the air bag upon initiation of the system response due to the occurrence of a collision and then the entire contents of the bag, comprising the gaseous products supplied by the inflator in admixture with the ambient atmosphere, is subsequently directed entirely out of the vehicle into the surrounding space. An example of this type of arrangement is illustrated in U.S. Pat. No. Re. 29,228 to Hass (i.e., a reissue of U.S. Pat. No. 3,632,133) wherein the air bag is inflated under the combined influence of a high velocity stream of gas produced by a pyrotechnic gas inflator device and a relatively large volume of air drawn into the bag by the passage of the high-velocity gas. The air may be drawn from outside the vehicle through a conduit assembly extending through the steering column, and subsequently discharged through the same conduit to the outside of the vehicle.
In addition, to facilitate the installation and maintenance of driver's side air bag assemblies, these systems have previously been produced in modular form, as described for example, in U.S. Pat. No. 3,819,205 to Dunford et al. Applicant is unaware, however, of any modularized air bag system which includes means, such as those described above, for aspirating ambient air, either from within or without the passenger compartment of the vehicle, and directing these additional gases into the air bag so as to facilitate the inflation thereof. Moreover, there is additionally no teaching in the prior art to vent the mixture from within the air bag component of such a modularized assembly completely out of the vehicle and into the surrounding space to facilitate deflation of the bag, while also avoiding the generation of an abrupt pressure increase within the vehicle which is known to be injurious to the occupants thereof.